The present invention relates to a power driving device and, more particularly, to a power driving device comprising a fluid coupling operated by an engine and a friction clutch disposed between the fluid coupling and a transmission.
A running gear for vehicles, which has a fluid coupling disposed in a drive system for absorbing rotational fluctuation and vibration of the engine, has been disclosed in, for example, Japanese Laid-open Patent Publication (Kokai) No. 164730/1980 (JP-A 55-164730). In the running gear for vehicles equipped with the fluid coupling, an engine mounted on the vehicle, the fluid coupling, a dry-type single-plate friction clutch and a transmission are arranged in series. The fluid coupling employed by the power driving device for vehicles includes a casing coupled to a crank shaft (input shaft as a fluid coupling) of, for example, a diesel engine, a pump disposed being opposite to the casing and mounted on the casing, and a turbine disposed being opposite to the pump and mounted on an output shaft arranged on the same axis as the input shaft, and an operation fluid for transmitting the torque is contained therein. The operation fluid generates heat as it circulates in the operation chamber formed by the pump and the turbine. In the fluid coupling disclosed in the above publication, therefore, the operation fluid is cooled by the air. There has also been employed a fluid coupling device of the operation fluid circulation type which radiates the heat by circulating the operation fluid.
There has been also proposed a fluid coupling equipped with a lock-up clutch which directly couples the input shaft and the output shaft together by bringing the casing into frictional engagement with the turbine. The lock-up clutch has a clutch disk which is placed between the casing and the turbine to form an outer chamber relative to the casing and to form an inner chamber relative to the turbine, and it is so constituted that the casing is engaged with, or disengaged from, the turbine by utilizing a pressure differential of the operation fluid circulating in the fluid coupling between the inner chamber side and the outer chamber side. In the fluid coupling equipped with this lock-up clutch, the direction of circulation of the operation fluid circulating in the fluid coupling is changed depending upon whether the lock-up clutch is in operation or not in operation.
A dry-type single-plate clutch is generally used as a friction clutch that is placed between the fluid coupling and the transmission. Meanwhile, use of a wet-type friction clutch may be conceivable in view of frictional wear of a clutch facing. When the wet-type friction clutch is used, an operation fluid is necessary for operating the clutch. The above-mentioned fluid coupling and the wet-type friction clutch are disposed in the housing.
The above-mentioned power driving device must be equipped with a fluid operation means for feeding the operation fluid that circulates through the fluid coupling and for feeding the operation fluid to the wet-type friction clutch. The fluid operation means includes a hydraulic pump which is a source of hydraulic pressure, a fluid passage for communicating the hydraulic pump with the fluid coupling and with the wet-type friction clutch, a relief valve for adjusting the pressure of the operation fluid blown out from the hydraulic pump, a control valve for changing over the fluid passage communicated with the fluid coupling, and a control valve for changing over the fluid passage communicated with the wet-type friction clutch. If piping such as pipes are used, the fluid operation means having these hydraulic pump, relief valve, control valves and fluid passage becomes too lengthy, requires a large space and extra amounts of operation fluid, and requires an increased number of parts and increased number of steps for assembly. It is therefore desired that the fluid operation means has a short fluid passage and is constituted in a compact size without using piping such as pipes.
It is therefore an object of the present invention to provide a power driving device which makes it possible to compactly constitute fluid operation means that circulates the operation fluid through the fluid coupling and that feeds the operation fluid to the wet-type friction clutch.
In order to solve the above-mentioned principal technical assignment according to the present invention, there is provided a power driving device comprising a fluid coupling having a pump operated by an engine and a turbine disposed being opposite to said pump, a wet-type friction clutch placed between said fluid coupling and a transmission, and a fluid operation means for circulating the operation fluid through said fluid coupling and for feeding the operation fluid to said wet-type friction clutch, said power driving device further comprising:
a coupling housing including a fluid coupling-holding chamber in which said fluid coupling is disposed and a friction clutch-holding chamber in which said friction clutch is disposed; and
a pump housing disposed in said coupling housing to partition said fluid coupling-holding chamber from said friction clutch-holding chamber;
wherein, in said pump housing, there is disposed a hydraulic pump that is driven by said pump of said fluid coupling and works as a source of hydraulic pressure for said fluid operation means, there are formed passages for communicating said hydraulic pump with said fluid coupling and with said wet-type friction clutch, and there are disposed a relief valve for adjusting the pressure of the operation fluid blown out from the hydraulic pump, a control valve for changing over the passage communicated with said fluid coupling and a control valve for changing over the passage communicated with said wet-type friction clutch.
It is desired that the relief valve and the control valves are disposed in the outer circumferential portions of the pump housing on the outer side of the outer circumference of the wet-type friction clutch in the radial direction. It is further desired that the relief valve and the control valves are constituted by spool valves comprising cylinder bores and spools slidably disposed in the cylinder bores, the cylinder bores being so formed that the axial directions thereof are perpendicular to the radial direction of the pump housing.